GEOLOGY OF THE LUZERNE QUADRANGLE 4I 



strata exhibit contortions. The many scattering bodies of Gren- 

 ville strata throughout the Adirondacks do not show any very per- 

 sistent strike as would be the case had they been subjected to 

 notable orogenic pressure. 



The structural relations of the Adirondack Grenville series are 

 reasonably explained as having been the result of slow, irregular 

 upwelling of the great bodies of more or less plastic magmas, prob- 

 ably under very moderate compression, whereby the strata, previ- 

 ously deformed little or none at all, were either broken up, tilted, 

 lifted or domed, or engulfed in the magmas. According to this 

 view, many large blocks or belts of Grenville strata, or several such, 

 rather locally separated by intrusive masses with strike of the 

 intrusives parallel to the strike of the Grenville, show monoclinal 

 dips; many masses of Grenville were shifted around in the irregu- 

 larly rising magmas and now show various strikes and dips accord- 

 ing to the directions of the magmatic currents; some bodies of 

 Grenville were merely arched-over bodies of laccolithically rising 

 magma so that they now exhibit more or less quaquaversal strikes 

 and dips ; some masses of strata were considerably bent or even 

 folded into synclines as a result of having been caught between 

 bodies of magma upwelling at about the same rate; some masses, 

 especially the more plastic limestones, were locally contorted near 

 the igneous contacts ; and many masses of strata were caught up 

 and enveloped by the rising magmas. 



The Grenville series of the Luzerne quadrangle, where it is free 

 from contamination with igneous materials, is too scantily repre- 

 sented by small scattering areas to throw much light upon its struc- 

 ture, but several of the more common types of occurrence above 

 mentioned are present. 



Another important fact is the practically universal parallelism of 

 foliation and stratification of the thoroughly crystalline Grenville. 

 Unless we assume intense isoclinal folding, as has been suggested 

 by Gushing, so that mineral elongation could everywhere have taken 

 place practically at right angles to the direction of lateral pressure, 

 the parallelism of stratification and foliation can not be accounted 

 for by crystallization under severe lateral pressure. In the paper 

 above cited, the writer has shown not only that there is no positive 

 evidence for isoclinal folding, but also that there is much evidence 

 against any more than mere tilting oi very moderate folding of the 

 Adirondack Grenville series. We thus conclude that Grenville 

 foliation was developed during crystallization of essentially hori- 



